With the high speed development of the 3rd Generation mobile communication technology (3G) network, the 1588 time synchronization protocol gets increasing attention and application in the communication network. The 1588 protocol is used by the domestic and foreign operators constantly to perform the time synchronization, to replace the use of the Global Positioning System (GPS) for the time synchronization progressively.
As shown in FIG. 1, in the 1588 time synchronization, the synchronous way is as follows: the following formulae can be obtained from FIG. 1:A=t1−t0=Delay+Offset;  (1)B=t3−t2=Delay−Offset;  (2)                and then the following formulae can be obtained according to the above (1) and (2):        a formula for Delay: Delay=(A+B)/2=((t1−t0)+(t3−t2))/2;        a formula for time offset: Offset=(A−B)/2=((t1−t0)−(t3−t2))/2.        
Wherein, the above-mentioned formulae suppose that time delays for the uplink and downlink are equal. The foundation of the 1588 time synchronization is to require a symmetrical delay for the uplink/downlink transmission. If the uplink/downlink transmission has the asymmetry, that is, when the delays of the uplink and downlink transmissions are unequal, as shown in FIG. 2, in this case, the 1588 protocol is used to calculate the time offset, half of the error value of the asymmetry has not be counted into the offset value, thus the time offset can not be corrected accurately and the quality of the time synchronization is reduced. Under the situation that the asymmetry delay is critical, even it will result in that the time is unable to be synchronized ultimately.
At present, mostly, the specialized test instruments are used to measure the delays of the 1588 uplink and downlink in the prior art. The actual value of the asymmetry delay is measured, and then the compensation is performed on the asymmetry delay through the 1588 asymmetry delay compensation method. However not only the method consumes the manpower and materials, but also the device cannot measure the actual asymmetry delay automatically when the link changes, thus reducing the quality of the time synchronization.